The secrets of plant cell structure

Chloroplasts and a cellulose cell wall are unique to plants – but plant cells have much in common with fungi, bacteria and animal cells too

How come plants can make their own food but animals can’t? It’s all down to the green, pigment-packed chloroplasts that help plants to turn carbon dioxide and water into glucose.

Modern-day chloroplasts were, according to endosymbiotic theory, once independent cells called cyanobacteria, which were incorporated into plant cells.

As they evolved into organelles, many of their genes were transferred into the plant cell genome. So although plants are eukaryotes, like animals, and their cells have many of the characteristics of eukaryotic cells – such as a nucleus containing chromosomes and mitochondria – their chloroplasts gives them an ability to photosynthesise that animal cells don’t have.

Plants do share one important feature with bacteria and fungi: a cell wall. Plant, bacteria and fungi cell walls have different compositions, but in plants, the wall is mostly made of cellulose. This long-chain molecule is made up of beta-glucose molecules covalently linked by glycosidic bonds that are difficult to hydrolyse (break down with the addition of water), providing strength and structure to the cell. Cellulose is thought to be the most abundant macromolecule on Earth.

In fungi, by contrast, the cell wall is made up of a mixture of long-chain molecules, including chitin (which also forms the exoskeletons of crabs), whereas in bacteria it is largely peptidoglycan-based.

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